* Gilead shares fell 4.8 percent after the drugmaker cut its full-year sales forecast, attracting a host of price target cuts. The stock was the top loser among S&P components.

* Wall Street ended lower on Monday as weak oil prices weighed on energy shares. Oil prices continued to be lower on Tuesday on oversupply worries.

* Investors will also keep an eye on economic data to judge the health of the U.S. economy. A report by Conference Board is likely to show the consumer confidence index slipped to 95.9 in July from 98.0 in June. The data is expected at 10:00 a.m. ET.

* Another report will show single-family homes sales rose 1.6 percent in June to 560,000. The report is due at 10:00 a.m. ET.